Question: Luis starts counting at 27, and he counts by fours. If 27 is the 1st number that Luis counts. what is the 13th number that he counts?
Solution: What is the first number that he counts? $27$ What is the second number that he counts? $\begin{align*}&27 + 4 \\ &= 31\end{align*}$ What is the third number that he counts? $\begin{align*}&27 + 4 + 4 \\ &= 27 + (2 \times 4) \\ &= 35\end{align*}$ What is the 13th number that he counts? $\begin{align*}&27 + (12\times4) \\ &= 27 + 48 \\ &= 75\end{align*}$